Comparative phytoremediation of chromium-contaminated soils by fenugreek, spinach, and raya

A glasshouse investigation was undertaken to evaluate the natural potential of fenugreek ( Trigonella foenumgraecum L.), spinach ( Spinacia oleracea L.), and raya ( Brassica campestris L.) for cleanup of chromium ( Cr) - contaminated silty loam and sandy soils. Four kilograms of soil per treatment in earthen pots was treated with five levels of chromium [ 0, 1.25, 2.5, 5.0, and 10.0 mg Cr kg(-1) soil through dipotassium chromate ( K2Cr2O7], equilibrated for 21 days at field- capacity moisture content, and then fenugreek, spinach, and raya were grown for 60 days after seeding. The concentration of diethylene triamine pentaacetic acid ( DTPA)- extractable Cr increased significantly with increasing rate of Cr application in both soils, but the increase was higher in sandy soil than in silty loam soil. The DTPA- extractable Cr in both soils decreased after harvesting of crops compared to its concentration in soil before sowing of the crops. The decrease in DTPA- extractable Cr concentration was highest in soil growing raya and least in the fenugreek- growing soil. The percent reduction in dry- matter yield ( DMY) with increasing levels of added Cr in comparison to the zero- Cr control was highest for fenugreek ( 49 and 52%) followed by spinach ( 36 and 42%) and lowest for raya ( 29 and 34%) in silty loam soil and sandy soil, respectively. Also, the percent reduction in mean shoot yield of all crops was higher in sandy soil ( 41%) compared to silty loam soil ( 36%), when the rate of applied Cr was increased from 0 to 10 mg Cr kg 21 soil. The DMY of both shoot and root was highest for raya and lowest for fenugreek. The Cr concentration in fenugreek, spinach, and raya increased with increasing level of added Cr in both soils. The concentration of Cr in both shoot and root was highest in raya, followed by spinach and fenugreek. The overall mean uptake of Cr in shoot was almost four times and in root was about two times higher in raya compared to fenugreek. The findings indicated that family Cruciferae ( raya) was most tolerant to Cr toxicity, followed by chenopodiacea ( spinach) and Leguminosae ( fenugreek). Because raya removed the highest amount of Cr from soil, it could be used for pytoremediation of mildly Cr- contaminated soils.